Ink jet head and method and manufacturing method thereof

ABSTRACT

The step of forming an electrode for external connection applies a conductive resin ( 10 ) to one end portion of each of a plurality of ink chambers ( 26 ) within each of the ink chambers ( 26 ) and to the top surface of each of a plurality of protrusions over a piezoelectric substrate ( 60 ) in one line perpendicular to the direction in which the ink chambers ( 26 ) extend. Subsequently, the conductive resin ( 10 ) located on the top surface of each of the plurality of ink chamber partitions is removed by polishing or grinding. As a result, the conductive resin ( 10 ) filling a space within each ink chamber ( 26 ) constitutes an electrode for external connection. This allows the capacitance due to the piezoelectric substrate to be decreased. Further, the driving frequency of the ink jet head can be increased. Thus, an ink jet head and its manufacturing method can be provided with a reduced power consumption, with an increased productivity and reliability and that allows a high speed printing.

TECHNICAL FIELD

The present invention relates to an ink jet head for an ink jet printerand a method for manufacturing the same.

BACKGROUND ART

In a conventional ink jet head, an external extension electrode extendsfrom an ink chamber electrode, which is provided within an ink chamber,to the outside of the ink chamber. The external extension electrode isconnected to an external circuit. The ink chamber electrode is thuselectrically connected with the external circuit.

A method of providing an ink chamber electrode of a conventional ink jethead extending to the outside of the ink chamber is described below withreference to FIG. 14.

First, one of the main surfaces of a piezoelectric element that has beenpolarized in the direction of its depth is laminated with a dry filmresist. The piezoelectric element is then halfway-diced using the dicingblade of a dicer. This forms an ink chamber 250 in the halfway-dicedportion. Moreover, removal of the dicing blade from the halfway-dicedpiezoelectric element leaves an arc portion 251 at the rear end of theink chamber. Halfway-dicing is further repeated for a plurality oftimes, producing a plurality of ink chambers 250 extending parallel toeach other.

This provides an ink chamber array 400 having a plurality of inkchambers 250. Subsequently, a metal that is to be an electrode material,such as Al or Cu, is deposited in an oblique manner in a direction thatis perpendicular to the direction in which the plurality of ink chambers250 extend and that is oblique with respect to a main surface of inkchamber array 400. This operation is made in two oblique directions withrespect to the direction of ink chambers 250. In this way, ink chamberelectrodes, each formed of a metal film 350, are formed on a surface ofink chamber partition 300. At this stage, the dry film resist and inkchamber partitions 300 between ink chambers 250 exhibit a “maskingeffect”. This provides a metal film 350 on an inner side of ink chamber250 with a height of less than about half that of the inner side of inkchamber 250.

Metal film 350 is also formed in the portion of the rear end of inkchamber 250 with a curved surface (arc portion) 251 and in the portionof opening of the dry film resist in a flat portion 260. Subsequently,only the dry film resist on flat portion 310 atop each ink chamberpartition 300 separating ink chambers 250 is removed, therebyestablishing, in arc portion 251, an electrical connection between thosemetal films 350 that are opposed to each other within ink chamber 250.

Subsequently, as shown in FIG. 15, a cover 210 with an ink supplythrough hole 209 is bonded to ink chamber array 400. In addition, anozzle plate 211 with nozzles 212 is bonded to ink chamber array 400.Thus, actuator 200 is obtained.

Actuator 200 provides for the Shear mode drive, where voltages inopposite phase are applied to the two respective ink chamber electrodes,each formed of one of opposing metal films 350 which is provided on therespective one of both inner sides of ink chamber partition 300separating ink chambers 250. This causes ink chamber partition 300 to bebent angularly on the border between the region having the ink chamberelectrode and the region without it, causing a change in the volume ofink chamber 250. This in turn causes a change in the pressure of inkwithin ink chamber 250. As a result, ink drops are ejected from verysmall nozzle 212 disposed at the tip end of ink chamber 250.

In the conventional structure of an ink jet head described above, activearea 252 that contributes to the ejection of ink is only located betweenink supply through hole 209 and the tip end. In other words, the regionbetween ink supply through hole 209 and the rear end does not contributeto ink ejection. Further, metal film 350 in arc portion 251 and flatportion 260 electrically connects those two ink chamber electrodes thatoppose each other in ink chamber 250. This provides an electricalconnection between an electrode that is conductive with a driving IC 115and metal film 350.

The above arrangement for ink jet heads suffers from the high materialcost due to an excessively large portion that is not included in activearea 252 which contributes to ink injection.

Moreover, the above ink jet head requires metal film 350 to extend fromwithin ink chamber 250 to flat portion 260 on the piezoelectricsubstrate of lead zirconate titanate (PZT) having a high dielectricconstant. This causes a large capacitance due to the piezoelectricsubstrate. This in turn disturbs the driving voltages applied to theactuator for driving it. Consequently, the frequency of the drivingvoltages must be reduced in the conventional ink jet head, which causesdifficulty in driving and printing at a high speed.

Disturbance in the waveform of the applied driving voltages may beovercome by increasing the voltages applied to the actuator. Increasingthe applied voltages, however, causes increase in the heat generated indriving the actuator to raise the temperature of the actuator itself.Thus, the conventional ink jet head suffers from a changing inkviscosity which makes a stable, precise printing impossible, anincreased cost of the driving IC with high applied voltages, and thedifficulty of reducing power consumption.

Accordingly, a conventional method of manufacturing ink jet headspreforms an Si—N film with a low dielectric constant between thepiezoelectric substrate and the ink chamber electrode in the portionthat is other than active area 252 of the ink chamber electrode withinink chamber 250 of the actuator. This achieves a negligible level ofcapacitance in the portion other than active area 250 using theconventional method. However, PZT has a low Curie point of about 200°C., requiring an electronic cyclotron resonance-chemical vapordeposition (ECR-CVD) device, which is very expensive, in order to forman Si—N film with a low dielectric constant on PZT using a process witha low temperature. As a result, the manufacturing cost is increased inthe conventional method such that inexpensive ink jet heads cannot beproduced.

A technique for coping with the above problems is disclosed in JapanesePatent Laying-Open No. 9-94954, which provides an ink jet head where, asshown in FIG. 16, the portion other than active area 252 is not locatedon an extension line of the ink chamber in the piezoelectric substrate.

In the described technique, an ink supply through hole 110 is providedat the rear end of the active area of the piezoelectric substrate tosupply ink. Each electrode 111 in the ink chamber extends externally onthe ink supply side of the substrate or extends to the area of the inkejection side of the substrate on its inner surface. This provides anelectrical connection of electrode 111 in the ink chamber with electrode112 which is conductive with a driving IC 115. In this case, no portionother than the active area for the actuator is provided on thepiezoelectric substrate, decreasing the material cost for thepiezoelectric substrate. However, an electrode 111 in the ink chamberextending externally on the ink supply side of the substrate orextending to the area of the ink ejection side of the substrate on itsinner surface still suffers from the problem that the capacitance due tothe piezoelectric substrate in the extending portion of ink chamberelectrode 111 cannot be reduced.

Moreover, in the above method, electrode 111 in the ink chamber extendsto be bent at 90° at a corner of the piezoelectric substrate forming theactuator.

The extension of an electrode to a side of an actuator requires a metalfilm to be provided on the side of the actuator such that thepiezoelectric substrate is divided into small individual actuators andan extension electrode is then put into continuity with the respectivepair of ink chamber electrodes. Further, a separation of the extendingelectrodes requires the steps of forming a uniform layer of conductorwith a resist pre-patterning and then separating it into electrodes bydicing or using yttrium aluminum garnet (YAG) laser. Consequently, theprocess is extremely complicated and thus productivity is low, reducingthe yield and increasing the production cost. Moreover, it is highlypossible that an extending electrode is broken up at a bended portion ofthe electrode which extends from within the ink chamber to a side of theactuator, during subsequent steps or transportation of the actuator,thereby decreasing the yield and the reliability in terms of theenvironment.

The extension electrodes may also be formed using plating. However, theplating technique requires, similar to deposition techniques, the stepsof patterning or dividing a material into electrodes. This maycomplicate the process.

Also, the above extension electrode as in FIG. 16 can be broken up at abended portion of the electrode extending from within the ink chamber toa surface of the actuator because of a botched handling duringsubsequent steps. Consequently, the conventional ink jet head has theproblems of decreased yield and less reliability in terms of theenvironment.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an ink jet head withreduced power consumption, improved productivity and reliability,capable of a high speed printing, and a method of producing the same.

An ink jet head of the present invention includes an ink chamberextending on the surface of a piezoelectric substrate from one to theother end, and driving electrodes provided within the ink chamber. Theink jet head further includes an electrode for external connection thatis connected to the driving electrodes and is also connected to anexternal electrode provided externally. Further, the electrode forexternal connection of the ink jet is composed of a conductive materialfilling an end portion of the ink chamber.

In a conventional ink jet head, the electrode for external connectionextends from within the ink chamber and along the surface of thepiezoelectric substrate exterior to the ink chamber when the ink chamberelectrode is mounted in the ink chamber. This is not necessary for theabove structure of an ink jet head.

Further, according to the above ink jet head, almost no portion isrequired other than the active area of the piezoelectric substrateforming the actuator. This can reduce the material cost of thepiezoelectric substrate.

Also, according to the above structure of an ink jet head, the electrodefor external connection does not need to extend from within the inkchamber and along the surface of the piezoelectric substrate exterior tothe ink chamber. This suppresses the increase in the capacitance due tothe extending portion of the electrode for external connection, wherebythe driving frequency can be improved. Thus, a high-speed printing isallowed.

Moreover, the driving voltages of the actuator do not need to beincreased to achieve a high-speed printing. Consequently, it is possibleto reduce the withstand voltages of the driving IC. Thus, according tothe above ink jet head, the cost of the driving IC and the powerconsumption for driving the driving IC can be reduced.

In the present ink jet head, the conductive material includes aconductive resin.

According to the above arrangement, a dispenser can be used inmanufacturing to apply a conductive resin. This facilitates themanufacture of the conductive material. In addition, warping of thepiezoelectric substrate can be minimized by mixing a conductive fillerwith a low extension material to reduce the coefficient of thermalexpansion of the conductive resin.

The conductive resin of the present ink jet head includes one or moreconductive filler(s) selected from the group consisting of Au, Ag, Ni,Cu, C, and solder.

According to the above arrangement, using Au or Ag for the conductivematerial can minimize the electrical resistance of the conductive resinand that between the conductive resin and the electrode that isconductive with the driving IC. This results in a possible improvementin the driving frequency of the voltages applied for driving theactuator. Thus, the above structure of an ink jet head provides ahigh-speed printing.

Alternatively, using Ni, Cu or C for the conductive material canminimize the cost of the conductive resin. Although this might cause adifficulty in achieving high-speed printing, it provides an extremelyeconomic actuator. In the case of solder, when establishing anelectrical connection to an external circuit, a solder filler is moltento allow a metal diffused junction, thereby establishing a connectionwith the external circuit electrode. Thus, a connection can beestablished with a high reliability and having a smaller value ofconnection resistance.

In the present ink jet head, each piece of the conductive filler has alongitudinal size ranging from 0.1 to 30 μm.

According to the above structure, pieces of conductive filler of theconductive resin have a relatively large contact area and aresufficiently large to serve as conductive resin; Thus, the electricalconductivity of the conductive resin can be improved without causingproblems.

In the present ink jet head, an electrode for external connection isformed by polishing or grinding the entire area of the top surface ofthe protruding wall defining the ink chamber.

Generally, after the conductive material deposited on the top of eachink partition is polished or grinded, the polishing rate becomesextremely small when the polishing or grinding member abuts against thetop surface of the partition. The above arrangement can take advantageof this to allow a reliable management of the position in which thepolishing should end.

In the present ink jet head, the electrode for external connection maybe formed by selectively polishing or grinding the top surface of eachprotrusion.

According to the above arrangement, there is no need to level warpingthat has occurred in the piezoelectric substrate as is the case that theentire surface of a piezoelectric substrate is treated. Thus, thepiezoelectric substrate only needs to be fixed on the dicing stage byvacuum absorption as in the normal dicing. This can simplify the processsignificantly.

In the present ink jet head, the selective polishing or grinding isperformed in the direction parallel to the direction in which the inkchambers extend.

According to the above arrangement, no force is generated that pullsapart the conductive material that is to be an electrode for externalconnection from a driving electrode. This improves the yield of the inkjet head.

In the present ink jet head, the selective polishing or grinding may beperformed in the direction perpendicular to the direction in which theplurality of ink chambers extend.

The above arrangement facilitates the selective polishing or grinding.

A method of manufacturing the present ink jet head includes the step offorming an ink chamber extending on a surface of a piezoelectricsubstrate from one to the other end, and the step of forming drivingelectrodes within the ink chamber. The method further includes the stepof forming an electrode for external connection connected to the drivingelectrodes and to an external electrode provided externally. The step offorming the electrode for external connection mentioned above furtherincludes the step of applying a conductive material to one end of theink chamber within the ink chamber and on the top surface of eachprotruding wall defining the ink chamber, and the step of removing theconductive material applied to the top surface of each protrusion on thepiezoelectric substrate.

According to the above method, the conductive material applied to theink chamber can integrate a plurality of electrodes within the inkchamber into one. At the same time, the cut surface of the appliedconductive material divided into small pieces or the exposed portionforming the surface of the applied conductive material provides forconnection with the external circuit. As a result, there is no need toform an actuator with a complicated structure. A simpler process is thusachieved.

Further, according to the above method, a dispenser may be used to applythe conductive material. The above method also allows, when using aconductive filler and a low expansion material mixed together, thecoefficient of thermal expansion of the conductive material to bereduced, thereby minimizing warping of the piezoelectric substrate.

In the present method, the step of removing the conductive materialincludes the step of removing the conductive material applied on the topsurface of each protrusion on the piezoelectric substrate usingpolishing or grinding.

According to the above method, conventional equipment and tools may beused to remove conductive material without difficulties.

In the present method, the polishing or grinding may be performed on theentire of the top surface of each protrusion.

According to the above method, polishing or grinding rates for theconductive material are different from those for the piezoelectricsubstrate. Accordingly, the time to terminate the polishing or grindingprocess can be readily identified taking advantage of the significantchange in the polishing or grinding rate.

In the present method, the polishing or grinding may include selectivelypolishing or grinding the portion of the top surface of each protrusionwhere the conductive material is provided.

According to the above method, there is no need to level warping thathas occurred in the piezoelectric substrate as is the case that theentire top surface of each protrusion over the piezoelectric substrateis treated. Therefore, the piezoelectric substrate can be just fixed tothe dicing stage by vacuum absorption without any disadvantages. Thisresults in a simpler manufacturing process.

In the present method, the selective polishing or grinding is performedin the direction parallel to the direction in which the ink chambersextend.

According to the above method, no stress is applied in the directionthat causes the conductive material that is to be an electrode forexternal connection to be pulled apart from the wall defining the inkchamber. Thus, the reliability of the continuity can be improved betweenthe conductive material and the ink chamber electrode.

In the present method, the selective polishing or grinding may beperformed in the direction perpendicular to that of the ink chambers.Such a method simplifies the polishing or grinding.

In the present method, the step of removing the conductive materialincludes the step of removing the conductive material by grinding usinga dicing or slicing machine.

According to the above method, the inventive grinding can be realized byonly replacing blades. As a result, no additional investment is requiredin equipment.

In the present method, the grinding using the dicing or slicing machinemay include chopping. Such a chopping process is advantageous in thatthe grinding process is simplified.

In the present method, in the case of having a plurality of ink chambersthat extend parallel to each other, the step of applying the conductivematerial may desirably include applying a conductive resin linearlycrossing the plurality of ink chambers perpendicularly. Such a methodfacilitates application of the conductive resin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an ink jet head of a first embodiment.

FIG. 2 is a cross sectional view taken along line II-II of FIG. 1.

FIG. 3 is a cross sectional view taken along line III-III of FIG. 1.

FIG. 4 is a cross sectional view of the ink jet head of the firstembodiment connected to a driving IC.

FIG. 5 is a cross sectional view taken along line V-V of FIG. 4.

FIG. 6 is a cross sectional view taken along line VI-VI of FIG. 4.

FIG. 7 is a perspective view of an ink jet head illustrating a method ofmanufacturing the ink jet head according to the first embodiment.

FIG. 8 is a perspective view of an ink jet head illustrating a method ofmanufacturing the ink jet head according to the first embodiment.

FIG. 9 is a perspective view of an ink jet head illustrating a method ofmanufacturing the ink jet head according to the first embodiment.

FIG. 10 is a perspective view of an ink jet head illustrating a methodof manufacturing the ink jet head according to the first embodiment.

FIG. 11 is a cross sectional view of the ink jet head illustrating themethod of the first embodiment.

FIG. 12 is a perspective view of an ink jet illustrating a method ofmanufacturing an ink jet head according to a second embodiment.

FIG. 13 is a perspective view of an ink jet head illustrating a methodof manufacturing an ink jet head according to a third embodiment.

FIG. 14 is a perspective view of a piezoelectric substrate of aconventional ink jet head.

FIG. 15 is a cross sectional view of another conventional ink jet head.

FIG. 16 is a cross sectional view of yet another conventional ink jethead.

BEST MODES FOR CARRYING OUT THE INVENTION

Now, an ink jet head and a method of manufacturing it according to theembodiments of the present invention will be described with reference tothe accompanying drawings.

First Embodiment

An ink jet head according to a first embodiment is described belowreferring to FIGS. 1-3.

The ink jet head of the present embodiment, as shown in FIGS. 1 and 2,has a conductive resin 10 containing an Ag conductive filler filling aspace between actuator driving electrodes 27 and 28 and close to rearend surface 21 of actuator 20 formed of a lead zirconate titanate (PZT)piezoelectric element.

In the area of rear end surface 21 of actuator 20, a cutaway end ofconductive resin 10 is exposed. Also, as shown in FIG. 2 showing a crosssection taken along line II-II of FIG. 1 and in FIG. 3 showing a crosssection taken along line III-III of FIG. 1, conductive resin 10 is alsoexposed in the area of top end surface 22 of that portion of ink chamber26 that is filled with conductive resin 10.

In each ink chamber 26, two actuator driving electrodes 27 and 28 areprovided, facing each other within ink chamber 26. Two electrodes 27 and28 are electrically connected via conductive resin 10 placedtherebetween.

A nozzle plate 25, having a very small nozzle 24, is attached to inkejection surface 23 of actuator 20. A cover 30 is provided that definesan ink supply through hole 31 at the rear of top end surface 22 ofactuator 20.

A plurality of ink chambers 26, disposed in an array, are separated byink chamber partition(s) 29 provided by the piezoelectric element.Actuator driving electrodes 27 and 28, each disposed on its respectiveink partition 29 and closer to top end surface 22, as well as conductiveresin 10 are integrated into one conductive resin electrode 11. When avoltage is applied to conductive resin electrode 11, actuator drivingelectrodes 27 and 28 are at the same potential with conductive resin 10.

Voltages of opposite phase are applied to actuator driving electrodes27, 28 and actuator driving electrodes 27′, 28′ opposite to them on theother side of ink chamber partition 29, in order to drive ink chamberpartition 29 using the Shear mode. The pressure of ink within inkchamber 26 is thus controlled to eject ink droplets through nozzle 24.

Further, in the ink jet head of the present embodiment, an exposedsurface of conductive resin 10 in the area of top end surface 22 ofactuator 20 is electrically connected to an external electrical circuitthrough anisotropic conductive film (ACF) 50, as shown in FIGS. 4-6,using an outer lead 42 on a tape automated bonding (TAB) tape 41, whichis conductive with driving integrated circuit (IC) 40.

An exposed surface of conductive resin 10 in the area of rear endsurface 21 of ink chamber 26 may also be electrically connected to anexternal electrical circuit. Conductive resin 10 may be formed from anAu plated bump, Au transferred bump or Au wall bump on outer lead 42.This bump conductive resin 10 may be pierced with outer lead 42 toelectrically connect conductive resin 10 with an external circuit. Thisprovides a more stable electrical connection, since outer lead 42 andconductive resin 10 have a greater contact area.

For an electrical connection path, the ink jet head of the presentembodiment uses a path through outer lead 42, conductive resin 10 andactuator driving electrodes 27, 28.

It is also possible to connect a protrusion electrode provided ondriving IC 40 directly with conductive resin 10 of the actuator. In thiscase, conductive resin 10 may be pierced with the protrusion electrode.This connection mode mounts a bare chip directly on the actuator,producing a smaller and more lightweight ink jet head. The aboveconnection mode also allows heat generated by the driving of driving IC40 to be conducted to the ink, thereby cooling driving IC 40.

Next, a method of manufacturing the ink jet head described above will beillustrated with reference to FIGS. 7 to 10. First, as shown in FIG. 7,one surface of piezoelectric substrate 60 that has been polarized in thedirection of its depths is laminated with a dry film resist 70.

A dicing blade of a dicer is then used to halfway-dice the piezoelectricwafer to form ink chamber 26. The width of the dicing blade correspondsto that of ink chamber 26.

After the ink chamber array is thus formed, a metal that is to be anelectrode material, such as Al and/or Cu, is deposited in an obliquemanner in a direction that is perpendicular to the direction in whichink chambers 26 extend and that is oblique with respect to a mainsurface of the ink chamber array.

This forms a metal film on each of both inner sides of ink chamberpartition 29. At this time, the films of dry film resist and ink chamberpartitions 29 exhibit the masking effect. Metal films are thus formed,each with a height of about half the height of ink chamber 26, measuredin the direction of the height of the chamber. The metal films formactuator driving electrodes 27 and 28.

Subsequently, the films of dry film resist are lifted off. Accordingly,no metal film for an electrode material described above remains atop inkchamber partition 29 of ink chamber 26. This ensures that ink chambers26 are electrically separated from each other.

Next, as shown in FIG. 8, a dispenser or the like is placed in thedirection perpendicular to the main surface of piezoelectric substrate60. In this way, conductive resin 10 is applied, 0.5 mm in width, to theinner surfaces of ink chamber 26 and the top face of ink chamberpartition 29 linearly traversing ink chambers 26 and ink chamberpartition 29.

Conductive resin 10 thus flows into ink chambers 26. Thus, actuatordriving electrodes 27 and 28 facing each other and each disposed on theupper portion of an ink chamber partition 29 are electrically connectedwith each other. Since conductive resin 10 is also applied on the topface of ink chamber partition 29, all actuator driving electrodes 27, 28are electrically connected.

Generally, conductive resin 10 is provided by mixing a conductive fillerand an adhesive. Pieces of conductive filler are provided contiguouslybetween actuator driving electrodes 27 and 28.

To ensure that conductive resin 10 that has flown in ink chamber 26electrically connects those actuator driving electrodes 27 and 28located on the inner sides of an ink chamber partition 29, a largenumber of pieces of conductive filler are required to be in connection.It is desirable, therefore, that each piece of conductive filler forconductive resin 10 has a longitudinal size of 0.1 μm-30 μm.

The electrical resistance between the pieces of conductive filler isexpected to vary depending on the properties of the conductive filler,the diameter of each piece of conductive filler, the adhesive viscosityof the conductive filler, the width of ink chamber 26, the width of theapplied conductive filler, and the contiguousness of the pieces ofconductive filler. Therefore, a centrifugal force is applied topiezoelectric substrate 60 to which conductive resin 10 has been appliedto ensure that the pieces of conductive filler are contiguous. In thisway, more conductive filler can flow in ink chamber 26. As a result,electrical connection between conductive resin 10 and actuator drivingelectrodes 27, 28 are more reliable.

The applied conductive resin 10 is then heated and cured. The heatingconditions depend on conductive resin 10. In the ink jet head of thepresent embodiment, the heating is desirably performed at a temperatureequal to or less than the Curie point of piezoelectric substrate 60 toprevent elimination of the polarization properties of polarizedpiezoelectric substrate 60 due to the heating.

Generally, conductive resin 10 has a coefficient of thermal expansiongreater than that of piezoelectric substrate 60. Consequently, afterconductive resin 10 is applied to ink chamber 26 and then cured,piezoelectric substrate 60 is warped to take a concave shape as viewedin a cross section perpendicular to the direction of the grooves of inkchambers 26. When a force is applied in subsequent steps to conductiveresin 10 in a direction that enables the warping to be leveled,conductive resin 10 may be pulled apart from actuator driving electrodes27, 28. As a result, conductive resin 10 may be electricallydisconnected with actuator driving electrodes 27, 28.

Accordingly, conductive resin 10 preferably has a coefficient of thermalexpansion close to that of piezoelectric substrate 60. Conductive resin10 has a conductive filler mixed together with a material that has acoefficient of thermal expansion smaller than that of piezoelectricsubstrate 60. Thus, the coefficient of thermal expansion of conductiveresin 10 is desirably reduced such that the coefficient of thermalexpansion of conductive resin 10 as a whole is closer to that ofpiezoelectric substrate 60.

Next, as shown in FIG. 9, conductive resin 10 which has been applied tothe top of ink chamber partition 29 is removed by polishing using apolishing member 70. This allows members that each form an ink chamberelectrode to be electrically separated. The polishing disk is positionedwith respect to an actuator wafer in such a way that a portion of thepolishing disk that comes in contact with the top surface (uppersurface) of ink chamber 29 moves in a direction parallel to that of inkchambers 26. This can suppress the delamination of actuator drivingelectrodes 27, 28 from ink chamber partition 29.

The polishing is performed in the steps of: leveling the warping thathas occurred in piezoelectric substrate 60; adhering the back surface ofthe leveled piezoelectric substrate 60 onto a highly flat plate usingwax; and polishing or grinding the top face of piezoelectric substrate60 using a wrapping surface plate or a cup abrasive. This removesconductive resin 10 which has been applied to the top of ink chamberpartition 29. This results in a structure shown in FIG. 10.

The area of conductive resin 10 applied to the top of ink chamberpartition 29 is smaller than that of the main surface of piezoelectricsubstrate 60. Consequently, when the polishing is finished (that is,electrical separation between ink chamber electrodes is completed), thearea for polishing increases dramatically. This causes the polishingrate to be significantly decreased. Thus, the position for finishing thepolishing can be managed by monitoring variations in the polishing rate.

The roughness of the polished surface is determined to provide for anadhesion of a cover wafer 61, as described below. Consequently, in themethod of the present embodiment, the polishing uses an abrasive ofapproximately No. 4000. The above steps allow each conductive resin 10in its respective ink chamber 26 to be electrically separated fromanother.

In the method of the present embodiment, the polishing allows eachconductive resin 10 in its respective ink chamber 26 to be electricallyseparated from another. Accordingly, the deposition of the electrodematerial to ink chamber partition 29 to form films can be performedwithout using dry film resist 70. Thus, actuator driving electrodes 27and 28 may also be formed atop ink chamber partition 29.

A cover wafer 61 as shown in FIG. 11 is prepared that is composed of apiezoelectric element with bores that are to be ink supply through holes31. Cover wafer 61 defines voids that serve as ink supply through holes31 after the subsequent steps to finish the ink jet head, and are to becover members 30 sealing ink chambers 26 at the top.

Normally, cover wafer 61 is desirably made of the same material as thatof the piezoelectric element defining ink chamber 26 in order to bettermatch it with the actuator defining ink chambers 26 in terms of thecoefficient of thermal expansion. However, cover wafer 61 may be formedof any material that has a coefficient of thermal expansion relativelyclose to that of the piezoelectric element defining ink chambers 26, forexample alumina ceramic.

Piezoelectric substrate 60 for the ink chamber array is then adhered tocover wafer 61 using a commercially available adhesive. At this point,each buried conductive resin 10 is positioned to be located at thecenter of the respective bore for ink supply through hole 31 in coverwafer 61. Piezoelectric substrate 60 is then bonded to cover wafer 61.

Fully-dicing is subsequently performed, using a dicing blade of a dicer,along the dicing lines indicated by broken lines in FIG. 11, in the areaof each of the ink supply through hole bores in cover wafer 61, in otherwords, in the area of each buried pressurized member 102 forming aprotrusion formed of conductive resin 10 in piezoelectric substrate 60.Piezoelectric substrate 60 and cover wafer 61 are thus divided intoindividual actuators.

At this stage, in the cut surface produced by the dicer, the cut surfaceof each conductive resin 10 is exposed as a side of the actuator. Thisprovides an electrode for external connection connected to an externalcircuit that is, in turn, connected to the driving IC. This results in afinished actuator.

Instead of conductive resin 10, a solder may fill a space betweenactuator driving electrodes 27 and 28 in the method of the presentembodiment. Solder has better physical properties than a conductiveresin in terms of connection between the external circuit and actuatordriving electrodes 27 and 28, and have a better electrical conductivity.This provides a more reliable connection between the external circuitand actuator driving electrodes 27, 28, while reducing variations in theelectrical resistance among ink chambers.

To form a solder electrode (not shown) in an ink chamber 26, solderpaste provided by mixing a flux and solder particles is supplied intoink chamber 26 using a dispenser or the like. Then, a laser beam isdirected to partially heat the solder, whereby solder is molten in theink chamber. As a result, the cut surface of the solder resulting fromthe dicing forms a contact surface between the solder electrode and theexternal electrode.

During the step of filling a space in ink chamber 26 with solder, aforced cooling is performed on the active area if necessary. This canprevent depolarization caused by the applied heat at the active area.

In the structure of the ink jet head of the present embodiment asdescribed above, the electrode for external connection is composed of aconductive resin filling a space within the ink chamber and apressurized member or a solder and pressurized member. Consequently,according to the ink jet head of the present embodiment, there is noneed for an extension electrode extending from the ink chamber electrodeto the outside. In addition, almost no portion other than the activearea of the actuator is necessary. Thus, the material cost can bereduced.

Moreover, in the ink jet head of the present embodiment, the electrodefor external connection does not have a portion extending along thesurface of the piezoelectric element. This can minimize the increase incapacitance due to a long electrode portion extending on the surface ofthe piezoelectric element. This can improve the driving frequency of theactuator. As a result, high-speed printing can be achieved. Further,according to the ink jet head of the present embodiment, high voltagesare not required to be applied to improve the driving frequency. Thiscan reduce the driving voltages for the driving IC. As a result, thepower consumption for the driving can be reduced.

In a conventional ink jet head, two or more independent electrodesopposite to each other within an ink chamber in an actuator for Shearmode driving need to be integrated into one driving circuit. Thisresults in an actuator with a large size and a complicated structure. Asa result, in a conventional ink jet head, a plurality of electrodeswithin an ink chamber need to be integrated into one for each inkchamber, while an extension electrode connected to the electrode withinthe ink chamber need to extend to a flat region on the actuator.

However, according to the method of the present embodiment, a conductiveresin or solder filling a space in the ink chamber may be used tointegrate a plurality of electrodes that were located outside the inkchamber into one. Also, in the actuator of the present embodiment, thefilling conductive resin, the cut surface of a solder or the surface ofthe filling solder is connected with the external circuit. Thus, anactuator with a complicated structure is not necessary. In this way, asimpler manufacturing process for an actuator can be achieved.

The electrode for external connection of a conductive resin is composedof Au, Ag, Ni, Cu, C or solder as conductive filler material of theconductive resin. Consequently, using Au or Ag for the conductive fillermaterial of the conductive material can reduce the electrical resistancein the conductive resin and the resistance in the connection to theelectrode conductive with the driving IC. As a result, the waveform ofapplied voltages for driving the actuator is not disturbed and thedriving frequency can be increased. In this way, high-speed printing canbe achieved. Alternatively, using Ni or Cu for the conductive fillermaterial of the conductive resin can reduce the cost of the conductiveresin. Although this may cause difficulty in printing at a high speed,it can provide a highly inexpensive actuator.

When a solder is used for the conductive filler material of theconductive resin, during establishing an electrical connection of theelectrode for external connection with an external circuit, a solderfiller is molten to allow a metal diffused junction, therebyestablishing a connection with the external circuit electrode.Accordingly, connection between the ink chamber electrodes can beestablished with a small value of connection resistance, whileestablishing a more reliable connection between ink chamber electrodes.

Further, when the ink chamber electrode is formed of Al, an oxide filmis formed on the surface of each ink chamber electrode made of Al.Accordingly, it is desirable to use a conductive filler with its pieceshaving a structure with an acute angle such as a needle, a flake or aspiked ball. Using a conductive filler having a structure with an acuteangle causes the oxide film to be partially destroyed during the step offilling with the conductive resin, in regions where the conductivefiller abuts against the ink chamber electrode of Al. This results in adecrease in connection resistance between the conductive resin and theink chamber electrode. Accordingly, the driving frequency of appliedvoltages can be increased without disturbing the waveform of appliedvoltages for driving the actuator. As a result, a high-speed printingcan be achieved.

In the electrode for external connection made of a conductive resin, theconductive filler is placed most densely within the conductive resinwhen using a conductive filler for the conductive resin with anapproximately round shape. The amount of the exposed conductive fillerper unit area on a cut surface of the conductive resin is thus at itsmaximum, reducing the value of connection resistance in the electricalconnection between the electrode for external connection and theexternal circuit. As a result, the driving frequency can be increasedwithout disturbing the waveform of applied voltages for driving theactuator, achieving a high-speed printing.

The electrode for external connection is desirably made of a conductiveresin having a glass transition point of 60° C. or more. In this case,sufficient reliability can be achieved at the storage and servicetemperatures for the ink jet head.

The electrode for external connection may be connected to the externalcircuit using an Sn based solder, which is a most readily available andinexpensive solder material, such that an ink jet head can be readilyprovided at low cost.

According to the ink jet head of the present embodiment using a solderfor an electrode for external connection, the number of added elementsand their amount can be easily reduced at the solder manufacturer.Further, the ink jet head of the present embodiment facilitates thecontrol of the melting point of the solder by, for example, increasingthe melting point of the solder depending on a temperature during themounting process of the external circuit. Thus, a novel actuator can bequickly developed and can be changed in its specification withoutdifficulties. In addition, when the electrode for external connection iscomposed of a solder material with a melting point of 80° C. or higher,a sufficient reliability can be accomplished at the storage and servicetemperatures for the ink jet head.

Second Embodiment

A method of manufacturing an ink jet head according to a secondembodiment of the present invention is described below with reference toFIG. 12.

The method for manufacturing the ink jet head of the present embodimentis different from that of the first embodiment in the manner in whichconductive resin 10 which has been applied to the top of ink chamberpartition 29 is removed. In the method of the first embodiment, aconductive resin cell applied to the top of each ink chamber partition29 is removed by polishing or grinding the entire top surface of eachink chamber partition 29 over piezoelectric substrate 60. On thecontrary, in the method of the present embodiment, conductive resin 10is removed by selectively polishing or grinding the region of each inkchamber partition 29 where conductive resin 10 is applied.

In the method of the present embodiment, similar to that of the firstembodiment, conductive resin 10 is applied to ink chamber 26 and inkchamber partition 29 in one line with a width of 0.5 mm using adispenser or the like in the direction perpendicular to that of inkchambers 26 of piezoelectric substrate 60, as shown in FIG. 8.Conductive resin 10 is subsequently cured. Next, as shown in FIG. 12,conductive resin 10 which has been applied to the top of ink chamberpartition 29 is selectively removed by moving a blade (abrasive) of adicing or slicing machine in the direction in which conductive resin 10was applied.

After conductive resin 10 which is located on the top surface of eachink chamber partition 29 has been removed, grinding is performed using ablade in the direction of the line in which conductive resin 10 wasapplied, to cut ink chamber partition 29 in the depth of 10-20 μm. Thisallows ink chambers 26 to be electrically separated.

The blade width Wb is greater than the width W of applied conductiveresin 10, and may be 1.0 mm. As a result of the blade machining, theportion of ink chamber partition 29 where conductive resin 10 is appliedhas a height that is smaller than that of the other portion of inkchamber partition 29 by 10-20 μm. Consequently, the grinded portion ofthe partition, with a width of 1.0 mm, does not contribute to adhesionwith cover wafer 61. Thus, the surface roughness of the grinded portionhaving a width of 1.0 mm does not need to be taken into account, suchthat the blade can be selected solely based on its ability in machiningduring the removal of conductive resin 10.

In the method of the present embodiment, the blade used for machiningincludes a diamond blade of No. 600. Thus, satisfactory grinding can beachieved without conductive resin 10 clogging the blade.

In the method of the present embodiment, not the entire top face of eachink chamber partition 29 over piezoelectric substrate 60 is polished orgrinded. Instead, only the portion of conductive resin 10 applied to thetop of ink chamber partition 29 is selectively polished or grinded to bemade flat. Accordingly, unlike the method of the first embodiment wherethe entire top face of each ink chamber partition 29 over piezoelectricsubstrate 60 is polished, there is no need to level warping ofpiezoelectric substrate 60. In addition, according to the ink jet headof the present embodiment, piezoelectric substrate 60 may be fixed tothe dicing stage by vacuum absorption as in a usual dicing without anydisadvantages.

Further, in the method of the present embodiment, the dicing or slicingmachine for forming ink chamber 26 is employed. Consequently, theinventive grinding can be realized just by replacing blades, eliminatingneed for investment in new equipment.

Third Embodiment

A method of manufacturing an ink jet head according to a thirdembodiment of the present invention is described below with reference toFIG. 13. The method of the present embodiment is different from those ofthe first and second embodiments in its way of removing conductive resin10. In the method of the second embodiment, ink chamber partition 29 iscut with a depth of 10-20 μm using a blade to perform the grinding inthe direction of the line in which the resin was applied to ink chamberpartitions 29 by a dispenser.

In the method of the present embodiment, conductive resin 10 is removedby selectively polishing or grinding the portion of conductive resin 10atop ink chamber partition 29 by chopping, in the directionperpendicular to the conductive resin cells applied to ink chamberpartitions 29 in one line by a dispenser (i.e. in the direction in whichink chambers 26 extend).

In the method of the present embodiment, similar to that of the firstembodiment, conductive resin 10 is first applied to ink chamber 29 andink chamber partition 29 in one line with a width of 1.0 mm, using adispenser or the like, in the direction perpendicular to the array ofink chambers 26 on piezoelectric substrate 60, as shown in FIG. 8.Conductive resin 10 is subsequently cured. Next, as shown in FIG. 13,conductive resin 10 which has been applied to the top of ink chamberpartition 29 is selectively removed by a chopping process using a blade(abrasive) of a dicing or slicing machine.

“Chopping” refers to a treatment performed by lifting and lowering ablade that is rotated at a high speed. The shape of the arc portionalong the periphery of the blade is transferred to the chopped portion.

During the chopping, conductive resin 10 is first removed in thedirection perpendicular to the line in which conductive resin 10 wasapplied to ink chamber partitions 29 by the dispenser (i.e. in thedirection in which ink chambers 26 extend). Subsequently, a portion ofink chamber partition 29 corresponding to the width of the blade is cutby a depth of 10-20 μm. Chopping is then repeated with a predeterminedpitch feed for selectively grinding the region of conductive resin 10.This removes conductive resin 10. This allows ink chambers 26 to beelectrically separated.

The desirable widths of the blade are such that one chopping can removeconductive resin 10 which is located atop each ink chamber partition 29.Consequently, it is more efficient to have a largest possible machiningsurface of the blade.

The shape of the outer diameter of the blade is transferred to theremoved region. Accordingly, the method of the present embodiment uses ablade having a chopping surface with a width of 2.5 mm and a diameter of2 inches.

The chopping rate is 5 mm/s. During chopping, the blade is lowered inthe direction perpendicular to the main surface of piezoelectricsubstrate 60 to cut each ink chamber partition 29 with a depth of 10-20μm. Therefore, the chopping process will not particularly increase theduration of the process.

The portion of ink chamber partition 29 where conductive resin 10 isremoved by the blade has a height that is smaller than that of the otherportion of ink chamber partition 29 by about 10-20 μm. Consequently, thegrinded portion due to the chopping does not contribute to adhesion withcover 61. The surface roughness of the grinded portion, therefore, doesnot need to be taken into consideration. As a result, the blade can beselected solely based on its ability in machining during the removal ofconductive resin 10.

In the method of the present embodiment, a diamond blade of No. 600 isused for grinding. This can achieve a satisfactory grinding withoutconductive resin 10 clogging the blade.

In the method of the present embodiment, not the entire top face of eachink chamber partition 29 over piezoelectric substrate 60 is grinded.Instead, only the portion of conductive resin 10 applied to the top ofink chamber 29 is selectively polished or grinded to be made flat.Consequently, it is not necessary to level warping of piezoelectricsubstrate 60 as in the case when the entire top face of each ink chamberpartition 29 over piezoelectric substrate 60 is polished or grinded.Moreover, in the method of the present embodiment, piezoelectricsubstrate 60 may be fixed to the dicing stage by vacuum absorption as ina usual dicing without any disadvantages.

In the method of the present embodiment, grinding is performed in thedirection perpendicular to the conductive resin 10 (the direction inwhich ink chambers 26 extend). Accordingly, no stress is applied in thedirection that would cause a conductive resin 10 applied to each inkchamber 26 and ink chamber partition 29 adhered thereto to be pulledapart. As a result, a more reliable continuity can be provided betweenconductive resin 10 and actuator driving electrodes 27 and 28.

A description of the blades and the grinding depths is provided below.

The blade used in the above experiments is of 2-3 inches in diameter,and the width W (in the direction in which ink chamber partitions 29extend) of applied conductive resin 10 ranges from 1.0 to 1.5 mm.Further, at least conductive resin 10 which has been applied to the topof each ink chamber partition 29 needs to be grinded away. Accordingly,taking the flatness of the piezoelectric substrate (±0.005 mm) intoaccount, the maximum of the grinding depth by the blade may be 20-30 μm.

A comparison among the methods of the above first to third embodimentsis provided below with reference to Table 1.

As shown in FIG. 9, when the entire top surface of each protrusion overthe piezoelectric substrate is polished, the disk is positioned withrespect to the piezoelectric substrate such that the direction of thepolishing by the rotated disk is generally parallel to the direction inwhich the top surface of each ink chamber partition extends. As aresult, although an ink jet head according to the manufacturing methodof the present embodiment has inferior ejection performances,practically no delamination between the ink chamber partition and theconductive resin occurs.

Referring to FIG. 12, the ejection performances are satisfactory whenthe grinding for removal of conductive resin is performed by a choppingin the direction perpendicular to the direction in which the top surfaceof each ink chamber partition extends. However, there is the possibilityof ink chamber partition being pulled apart from the conductive resin.

Referring to FIG. 13, when the grinding for removal of conductive resinis performed by a chopping in the direction parallel to the direction inwhich the top surface of each ink chamber partition extends, theejection performances were satisfactory and practically no delaminationbetween the ink chamber partition and the conductive resin occurred.

Consequently, it is desirable to perform the grinding for removal ofconductive resin in the direction parallel to the direction in which thetop surface of each ink chamber partition extends, as shown in FIG. 13.TABLE 1 Ejection (Comparative Grinding Performances Grinding GeneralExamples) Area etc. Direction Cracks Evaluation The method of Entire XParallel ◯ Δ surface The method of Partial ◯ Perpendicular X Δ Themethod of Partial ◯ Parallel ◯ ⊚

It should be understood that the disclosed embodiments above are, in allrespects, by way of illustration and example only and are not by way oflimitation. The scope of the present invention is set forth by theclaims rather than the above description and is intended to include allthe modifications within the spirit and scope equivalent to those of theclaims.

Industrial Applicability

The present invention, as described above, provides an ink jet head witha reduced power consumption, with an improved productivity andreliability and that allows a high-speed printing.

1. An ink jet head comprising: an ink chamber provided to extend on asurface of a piezoelectric substrate from one end to the other end; adriving electrode provided within the ink chamber; and an electrode forexternal connection connected to the driving electrode and connectableto an external electrode provided externally, wherein the electrode forexternal connection is composed of a conductive material filling one endportion of said ink chamber.
 2. The ink jet head according to claim 1,wherein said conductive material includes a conductive resin.
 3. The inkjet head according to claim 2, wherein said conductive resin includes aconductive filler, and the conductive filler includes one or morematerials selected from the group consisting of Au, Ag, Ni, Cu, C andsolder.
 4. The ink jet head according to claim 3, wherein each piece ofsaid conductive filler has a longitudinal size of at least 0.1 μm and atmost 30 μm.
 5. The ink jet head according to claim 1, wherein saidelectrode for external connection is formed by polishing or grinding theentire area of a top surface of a protruding wall defining said inkchamber.
 6. The ink jet head according to claim 1, wherein saidelectrode for external connection is formed by selectively polishing orgrinding part of a top surface of a protruding wall defining said inkchamber.
 7. The ink jet head according to claim 6, wherein saidselective polishing or grinding is performed in a direction parallel tothe direction in which said ink chamber extends.
 8. The ink jet headaccording to claim 6, wherein said selective polishing or grinding isperformed in a direction perpendicular to the direction in which saidink chamber extends.
 9. A method of manufacturing an ink jet head,comprising the steps of: forming an ink chamber extending on a surfaceof a piezoelectric substrate from one end to the other end; forming adriving electrode within said ink chamber; and forming an electrode forexternal connection connected to said driving electrode and connected toan external electrode provided externally, wherein said step of formingthe electrode for external connection includes the steps of: applying aconductive material to one end of said ink chamber within said inkchamber and to a top surface of a protruding wall defining said inkchamber; and removing that conductive material which has been applied tothe top surface of each protrusion over said piezoelectric substrate.10. The method of manufacturing an ink jet head according to claim 9,wherein said step of removing conductive material includes removing thatconductive material which has been applied to said top surface bypolishing or grinding.
 11. The method of manufacturing an ink jet headaccording to claim 10, wherein said polishing or grinding includespolishing or grinding the entire area of said top surface. 12.(Canceled)
 13. (Canceled)
 14. The method of manufacturing an ink jethead according to claim 10, wherein said polishing or grinding includesselectively polishing or grinding a portion of said top surface wheresaid conductive material is provided.
 15. The method of manufacturing anink jet head according to claim 14, wherein said selective polishing orgrinding is performed in a direction parallel to the direction in whichsaid ink chamber extends.
 16. The method of manufacturing an ink jethead according to claim 14, wherein said selective polishing or grindingis performed in a direction perpendicular to the direction in which saidink chamber extends.
 17. The method of manufacturing an ink jet headaccording to claim 9, wherein said step of removing conductive materialincludes removing said conductive material by grinding using a dicing orslicing machine.
 18. The method of manufacturing an ink jet headaccording to claim 17, wherein said grinding using the dicing or slicingmachine includes chopping.
 19. The method of manufacturing an ink jethead according to claim 9, wherein, when a plurality of ink chambers areprovided extending parallel to each other, said step of applyingconductive material includes applying said conductive resin linearlytraversing said plurality of ink chambers perpendicularly.